According to Hinduism, What is the ultimate goal of existence?

Not all Hindu sects believe that the ultimate goal is to be united with Brahman. This is the path of knowledge. There are other paths e. g devotion, that led to union with a personal God. Achieving union with Brahman is not really becoming anything else.

The ultimate goal for those who are Hindu is to attain something that is called moksha, it mean to be freed from the cycle or births in this world. Someone who attains moksha will join Brahman, or they might choose to be born again / in other words to be reincarnated